Aggregate Freight Generation Modeling

Abstract

The most comprehensive publicly available freight databases are the Commodity Flow Survey and FHWA's Freight Analysis Framework. These two sources contain the dollar value and weight of freight movements at high geographic levels, such as states or metropolitan areas. Because of the difficulty of obtaining freight data at lower geographic levels, various practitioners and researchers have suggested estimating freight models on the basis of aggregate data. Following recent practice, a methodology is presented to estimate a nationwide production and attraction model for U.S. domestic trade of goods. To this end, a Commodity Flow Survey data set provided by the U.S. Census Bureau and composed of a 2-nonconsecutive-year period (2002 and 2007) of goods movement between U.S. states for 27 industry sectors was used. The state payroll by industry sector, obtained from the County Business Patterns of the U.S. census, was the variable used to estimate freight generation models. The main objective of this study was to analyze the temporal stability and predictability of the proposed aggregate models. The results indicate that payroll alone explains a significant portion of the freight production and attraction at the state level. However, such simplification in the model process did not result in reasonable predictions of freight for a future-year horizon. It is recommended that time-dependent factors (e.g., variables related to changes in industry productivity) affecting freight demand be considered in the modeling process.